A P30, the major surface antigen of the T. gondii tachyzoite stage, has been isolated and shown to protect mice from a virulent T. gondii challenge. In Phase I of this project, the genomic DNA encoding P30 has been subcloned into Sindbis virus vectors and expressed in baby hamster kidney (BHK) cells. The recombinant proteins expressed from these Sindbis vectors were recognized with monoclonal antibody (MAb) against P30 by immunoblot analysis. Additionally, polyvalent sera against either native P30 or against T. gondii tachyzoite and several MAbs against P30 recognized glutathione-S-transferase (GST) fusion protein expressed by a Sindbis GST-P30 construct in immunoblot analysis.Conversely, polyvalent anti- Sindbis expressed GST-P30 fusion protein serum reacted specifically with native P30 protein and T. gondii tachyzoite lysate. Sindbis virus vectors were also demonstrated to be able to express another parasite antigen. The specific aim of this Phase II proposal is to demonstrate that the recombinant P30 protein expressed by Sindbis virus vectors can protect mice against a lethal challenge with virulent T. gondii. Success will lead to studies of this recombinant vaccine in food animals. The ultimate aim is commercial development of vaccines to prevent toxoplasmosis in food animals and humans. In addition, these studies will extend the experimental and practical utility for the development of other vaccines based on this live Sindbis vector technology.